MacAnulty, Cust, and Knott all suffer from the same problem: their best position is DH. None is likely to supplant Gonzalez at 1B, and none is adequate at the outfield corners. Johnson has proven himself at the AAA level, and can play all three OF positions. This one is a no-brainer.

In regards to P-Mac, I'd prefer to have stuck him at 3B, hoping for a .370-.470 OBP-SLG line, and suffered with the defense, than acquire T. Walker to further cloud the situation.